The present invention relates to systems for measuring the transmission of light through optical systems and, in particular, to systems for measuring the attenuation of light transmitted through an eyeglass lens.
Optical systems, such as eyeglasses, are commonly designed to filter portions of the light spectrum. For example, eyeglass lenses are frequently designed to attenuate the transmission of light in wavelengths that cause discomfort to the wearer or damage to the eyes—e.g., wavelengths corresponding to UV and/or high energy visible light (e.g., blue light). However, not all high energy visible light is harmful. Certain wavelengths of blue light are believed to be important for regulation of circadian sleep/wake cycles. Consequently, such lenses may have complex filtering properties—e.g., may only attenuate certain wavelengths and/or have varying degrees of attenuation over a range of wavelengths corresponding to blue light.
Eyeglass lens designs that block similar portions of the spectrum can be difficult to differentiate. The filtering properties of eyeglass lenses are typically measured in a laboratory setting, and the test results are not provided in real time and may not be accessible to an eyecare professional or eyeglass wearer. Furthermore, lens performance is often reported in broad terms (e.g., 100% UV protection), or using different standards or scales that cannot easily be compared. Such information may not be sufficient to fully understand the complex filtering properties of a lens, or to adequately differentiate between lenses with similar features.
In addition, laboratory testing is commonly performed under optimal conditions that fail to take into account the performance of eyeglasses under actual conditions of use. Laboratory tests typically involve the use of unfinished or semifinished lens blanks, and measure the transmission of a brief flash of light from a pin point source along an axis centered on and normal to the lens surface. Such tests do not reflect actual conditions of general lighting or sunlight, and may not provide a useful measure of transmission of the solar spectrum. Furthermore, eyeglass lenses are ground to prescription and are fitted to an eyeglass frame to accommodate the wearer's face and head geometry, which may factor in the transmission of light through the lens. The eyeglass lenses are generally held in the eyeglass frame at a slight tilt around a horizontal axis relative to the primary gaze angle (pantoscopic tilt), and may also have tilt around a vertical axis relative to the primary gaze angle (panoramic angle or wrap angle). The position of the pupil on the eyeglass lens (optical center) is commonly displaced from the center of the eyeglass frame. Eyeglasses may also take into account the distance between the wearer's cornea and the back of the lens (vertex distance). Such fitting parameters are commonly referred to as “position of wear”.
Therefore, there is a need for a system for measuring the transmission of light through eyeglasses or other optical systems that provides detailed spectral data in real time. It would also be desirable to provide a system that measures the transmission of light taking into account the position of wear of the eyeglasses.